This disclosure relates in general to measurement of nip force in a nip formed by a pair of rollers in a printing system, and, in particular to an apparatus and method which are capable of determining the nip width distribution between nipped rollers.
The nip width is the measured arc distance created by the intersection of a soft fuser roll and a hard pressure roll (nipped rolls) in an image production device, such as a printer, copier, multi-function device, and the like, which enables heat transfer and pressure needed to fuse prints. Nipped rolls are used in a vast number of continuous process industries including papermaking, steel making, plastics calendaring and printing. In the printing space, variation of the nip width from optimal conditions can cause toner to be improperly melted and pressed (fused) against the print media resulting in image quality defects. In addition, improper nip setting can result in excessive wear of the fuser roll surface which results in image quality defects in the form of areas containing unacceptable differential gloss.
An accurate and consistent nip width increases fuser roll life by helping to minimize edge wear on the roll. It has been shown that uneven and excessive nip settings, inboard to outboard, result in accelerated edge wear. The nip width is supposed to be checked and adjusted with every fuser roll replacement. This measurement is not always done and combined with roll Durometer varying significantly from batch to batch, the roll nip widths are frequently incorrectly set. In addition, as the fuser roll ages the softness of the rubber changes resulting in less-than-optimum nip widths.
Methods have been used to discover discrepancies in nip width as a function of applied pressure. One such method known as taking a nip impression requires stopping the roll and placing a long piece of carbon paper, prescale film, foil, or impressionable film in the nip. This requires the operator to load the rolls carefully to ensure that both sides, that being front and back, are loaded evenly. The pressure in the nip transfers a carbon impression, deforms the foil, or ruptures ink containing capsules in the film, indicating the width of contact. These methods offer only a single event such as the highest pressure or contact width, are susceptible to temperature and moisture variations, and if done at every print would negatively impact the printing process.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification there is need in the art for apparatus, and/or methods that can dynamically measure nip width.